Secure communication is the first and foremost requirement in modern everyday life, be it in transfer of money to bank through a third party application, military applications, national security and other fields of daily lives that are totally dependant upon the internet for transfer of data from one node to another. Exploiting the properties of Quantum mechanics along with various protocols designed for communication, there is a possibility of communicating quantum information from Alice to Bob securely. Traditional classical communication in today's world uses various encryption protocols, such as Shor's factoring algorithm [1]}, Lov Grover's algorithm [2]} and RSA protocols [3]}. The basic difference between quantum and classical communication is that, any attempt to hack the system will be detected on-site in case of quantum communication. Thus, privacy of quantum communications is preserved by different modes such as QKD [4]}, quantum secret sharing (QSS) [5]}, quantum secure direct communication (QSDC) [6]}, quantum teleportation [7]} and quantum dense coding [8]}. Currently used classical cryptosystems, such as RSA, can be cracked with quantum computers in market, putting all the security systems at a risk. But among all these schemes, QKD is provably secure mode of communication and lot of researchers are interested in developing QKD protocols for secure communication. QKD systems basically follows number of protocols for providing security and integrity to data which was discussed earlier in Section IV-E. QKD has been researched widely, and successfully applied to a distance covering few hundreds of kilometers [9]}. This distance has been extended to 1200 Kms with the launch of Micius satellite by chinese scientists [10]}. This is a breakthrough in the research of quantum internet as before this satellite was launched, this distance was limited to few hundreds of kilometers. Therefore a lot of research is going on satellite-based quantum communications by Europe, USA, Canada, Japan, and Singapore [11]}. The distance of 500 Kms has been achieved recently in case of low-loss fiber based channels [12]}, [13]}.
